According to the Glossary of Meteorology, a funnel cloud is any rotating cloud pendant from a cumulus or cumulonimbus, and thus most tornadoes are included under this definition.
Among many meteorologists, the 'funnel cloud' term is strictly defined as a rotating cloud which is not associated with strong winds at the surface, and condensation funnel is a broad term for any rotating cloud below a cumuliform cloud.
Although the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 40 mph (64 km/h), the circulation is considered a tornado.
A tornado with a nearly cylindrical profile and relative low height is sometimes referred to as a "stovepipe" tornado.
Tornadoes may be obscured completely by rain or dust.
These tornadoes are especially dangerous, as even experienced meteorologists might not see them. Small, relatively weak landspouts may be visible only as a small swirl of dust on the ground.
The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles (more than 100 km).
Various types of tornadoes include the multiple vortex tornado, landspout, and waterspout.
Several tornadoes are sometimes spawned from the same large-scale storm system.
If there is no break in activity, this is considered a tornado outbreak (although the term "tornado outbreak" has various definitions).